The grandmother of slain baby Sema'j Crosby said that a couple days after she took the stage in a church on Chicago's South Side and accused the child's mother of having a hand in her daughter's death.

“In my heart, I feel as though she did do this,” Darlene Crosby said.

Back in April, Sema'j was found dead under the couch in her Preston Heights home. The police had been searching for the little girl for a day and a half, combing through fields and ponds after the baby's mother, Sheri Gordon, called 911 to report her daughter missing.

It took months for the authorities to figure out how Sema'j died. They said in September it was suffocation but still don't know how it happened. They also have yet to pin down how she got under the couch or who put her there.

The grandma, who sometimes calls Sema'j “Tink,” may not have all the details nailed down but believes she has uncovered the motive behind the crime.

“It was spiteful and to get back at my son,” who is Sema'j's father, Darlene Crosby said.

The father, James Crosby, has another child with Gordon as well, Darlene Crosby said, but has “moved on and started a life with his new family.”

“It was more like Sheri, in Sheri's mind, there's only one woman for my son,” Darlene Crosby explained. “Sheri was heartbroken he moved on. Sheri could never let go.”

And that's why Darlene Crosby thinks Sheri Gordon had something to do with Sema'j ending up dead and under a couch. We know Sema'j's father couldn't have done it, as he was in jail. And the way Darlene Crosby tells it, she and her friend Tamika Robinson and her daughter, Lakerisha Crosby, are in the clear because they weren't even in the house.

“I don't know how (Sheri Gordon) did it,” Darlene Crosby said. “I do know: four people. One in the house. Three outside. Four minus three is one. It's not that hard to figure out.”

The attorney for Sheri Gordon, Neil Patel, said Darlene Crosby's accusations make no difference to the way he is handling the matter. He also referred to a statement on his law firm's Facebook page that said, “Ms. Gordon, through her attorneys, continues to strongly deny any statement or inference that suggests she knew of or caused (Sema'j's) death or concealed her death.”

It also said "no one wants to know what happened to (Sema'j) more than her mother.”

Darlene Crosby claims Sheri Gordon has held herself out there as if she already knows what happened and has made some accusations of her own.

“As the time went on, the detective came and got me (the day after Sema'j disappeared) and said, 'You know, what if I said that Sheri said I may have hurt Tink because I thought DCFS was going to take her,” Darlene Crosby said when she was at the church. “And from that point on, I knew that Sheri was starting to blame.”

And Sheri Gordon wasn't just blaming her, said Darlene Crosby, who claimed Gordon also “tried” to blame Tamika Robinson, somebody named Coolie and “another person around the corner from Tamika's house — I don't want to say this person's name.”

“I have nothing to hide, I'm telling the truth,” said Darlene Crosby, who also insisted, “I have not lied about one thing.”

And maybe she hasn't. But she also failed a polygraph, said Lt. Dan Jungles of the Will County Sheriff's Office. Darlene Crosby blamed this on the police's “tactics.”

“Although polygraph machines look scientific and measure responses such as sweating and increased pulse rate with exquisite accuracy, they are crude in their conception,” said a Psychology Today article that compared the polygraph to an “ancient Arab ordeal for detecting liars.”

“In the Arab test, a heated knife blade was pressed to the subject’s tongue,” the story said. “If he was telling the truth, his tongue would not get burned. The idea is that when people are nervously excited, their mouth goes dry because nervousness suppresses salivation. In principle, the lie detection system involved is exactly the same as for a polygraph test.

Whether the lie detector tells you anything or not, Jungles said Darlene Crosby was definitely less than truthful when she told of the police's lack of interest in speaking with her.

“I've tried to call the detective, I left him messages on the stuff that a person was doing, and wanted to see stuff, and they're not talking to me, and they're not talking to my lawyer,” she said.

Jungles had a different take on Darlene Crosby's relationship with the police.

“Once Darlene took the polygraph exam and she failed it, she basically stormed out of here and we basically haven't spoken to her since,” he said. “And we tried.”

Darlene Crosby said she has a lawyer, Cosmo Tedone, who you think would have advised her against appearing at press conferences, at least without having him around.

Tedone failed to return calls about it this week. Jungles suspects Darlene Crosby and Tamika Robinson spoke because they “both have their own agendas in getting their sides out.”

And it didn't hurt to keep Sema'j's name out there either. She's been dead now nearly seven months. A group has been trying to get a park named after her but the park district doesn't seem to be in much of a hurry to make it happen.

Whether they name the park after her or not, the detectives don't need reminders of what happened to Sema'j.

“What happened was a horrible thing,” Jungles said. “No child should be stuffed under a couch. We're not going to stop until someone is held accountable.”

• Joe Hosey is the news editor at The Herald-News. You can reach him at jhosey@shawmedia.com, 815-2804094 or on Twitter @JoeHosey.